mirror of https://github.com/SixLabors/ImageSharp
James Jackson-South
1 week ago
2 changed files with 169 additions and 0 deletions
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// Copyright (c) Six Labors.
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// Licensed under the Six Labors Split License.
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using SixLabors.ImageSharp.Memory; |
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namespace SixLabors.ImageSharp.Formats.Heif.Hevc; |
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/// <summary>
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/// Stores the spatial coding-unit state required by later HEVC still-picture syntax and reconstruction stages.
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/// </summary>
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internal sealed class HevcCodingTreeState : IDisposable |
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{ |
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/// <summary>The coding-unit flag indicating transform and quantization bypass.</summary>
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private const byte TransquantBypassFlag = 1 << 0; |
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/// <summary>The coding-unit flag indicating pulse-code-modulated samples.</summary>
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private const byte PcmFlag = 1 << 1; |
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/// <summary>The decoded coding-unit depth at minimum-coding-block resolution.</summary>
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private readonly Buffer2D<byte> depths; |
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/// <summary>The effective luma quantization parameter at minimum-coding-block resolution.</summary>
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private readonly Buffer2D<sbyte> quantizationParameters; |
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/// <summary>The packed bypass and PCM flags at minimum-coding-block resolution.</summary>
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private readonly Buffer2D<byte> flags; |
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/// <summary>
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/// Initializes a new instance of the <see cref="HevcCodingTreeState"/> class.
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/// </summary>
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/// <param name="configuration">The configuration providing the image memory allocator.</param>
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/// <param name="sequenceParameterSet">The coded picture and minimum coding-block geometry.</param>
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public HevcCodingTreeState(Configuration configuration, HevcSequenceParameterSet sequenceParameterSet) |
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{ |
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this.MinCodingBlockLog2 = sequenceParameterSet.MinCodingBlockLog2; |
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this.WidthInMinCodingBlocks = DivideCeilingByPowerOfTwo( |
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sequenceParameterSet.Width, |
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this.MinCodingBlockLog2); |
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this.HeightInMinCodingBlocks = DivideCeilingByPowerOfTwo( |
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sequenceParameterSet.Height, |
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this.MinCodingBlockLog2); |
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this.depths = configuration.MemoryAllocator.Allocate2D<byte>( |
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this.WidthInMinCodingBlocks, |
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this.HeightInMinCodingBlocks); |
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this.quantizationParameters = configuration.MemoryAllocator.Allocate2D<sbyte>( |
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this.WidthInMinCodingBlocks, |
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this.HeightInMinCodingBlocks); |
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this.flags = configuration.MemoryAllocator.Allocate2D<byte>( |
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this.WidthInMinCodingBlocks, |
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this.HeightInMinCodingBlocks); |
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} |
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/// <summary>Gets the base-two logarithm of the state map's luma sample unit.</summary>
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public int MinCodingBlockLog2 { get; } |
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/// <summary>Gets the state-map width in minimum coding blocks.</summary>
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public int WidthInMinCodingBlocks { get; } |
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/// <summary>Gets the state-map height in minimum coding blocks.</summary>
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public int HeightInMinCodingBlocks { get; } |
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/// <summary>Gets the split-flag context derived from available left and above coding units.</summary>
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/// <param name="x">The current coding-unit left coordinate in luma samples.</param>
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/// <param name="y">The current coding-unit top coordinate in luma samples.</param>
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/// <param name="depth">The current coding-tree depth.</param>
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/// <param name="leftAvailable">A value indicating whether the left coding unit is available for prediction.</param>
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/// <param name="aboveAvailable">A value indicating whether the above coding unit is available for prediction.</param>
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/// <returns>The split context in the inclusive range zero through two.</returns>
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public int GetSplitContext(int x, int y, int depth, bool leftAvailable, bool aboveAvailable) |
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{ |
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int unitX = x >> this.MinCodingBlockLog2; |
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int unitY = y >> this.MinCodingBlockLog2; |
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int context = 0; |
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if (leftAvailable && this.depths.DangerousGetRowSpan(unitY)[unitX - 1] > depth) |
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{ |
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context++; |
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} |
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if (aboveAvailable && this.depths.DangerousGetRowSpan(unitY - 1)[unitX] > depth) |
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{ |
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context++; |
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} |
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return context; |
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} |
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/// <summary>Records the state shared by every minimum coding block covered by one leaf coding unit.</summary>
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/// <param name="x">The coding-unit left coordinate in luma samples.</param>
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/// <param name="y">The coding-unit top coordinate in luma samples.</param>
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/// <param name="log2Size">The base-two logarithm of the square coding-unit size.</param>
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/// <param name="depth">The coding-tree depth.</param>
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/// <param name="quantizationParameter">The effective luma quantization parameter.</param>
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/// <param name="transquantBypass">A value indicating whether transform and quantization are bypassed.</param>
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/// <param name="pcm">A value indicating whether the coding unit contains pulse-code-modulated samples.</param>
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public void SetCodingUnit( |
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int x, |
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int y, |
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int log2Size, |
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int depth, |
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int quantizationParameter, |
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bool transquantBypass, |
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bool pcm) |
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{ |
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int unitX = x >> this.MinCodingBlockLog2; |
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int unitY = y >> this.MinCodingBlockLog2; |
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int unitCount = 1 << (log2Size - this.MinCodingBlockLog2); |
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int endX = Math.Min(unitX + unitCount, this.WidthInMinCodingBlocks); |
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int endY = Math.Min(unitY + unitCount, this.HeightInMinCodingBlocks); |
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byte packedFlags = (byte)((transquantBypass ? TransquantBypassFlag : 0) | (pcm ? PcmFlag : 0)); |
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// Edge coding units still cover a complete power-of-two block in syntax, but the state map contains only
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// displayed picture coordinates. Clipping here keeps later neighbor lookup within the owned picture state.
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for (int row = unitY; row < endY; row++) |
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{ |
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this.depths.DangerousGetRowSpan(row)[unitX..endX].Fill((byte)depth); |
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this.quantizationParameters.DangerousGetRowSpan(row)[unitX..endX].Fill((sbyte)quantizationParameter); |
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this.flags.DangerousGetRowSpan(row)[unitX..endX].Fill(packedFlags); |
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} |
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} |
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/// <summary>Gets the recorded coding-tree depth at a luma sample coordinate.</summary>
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/// <param name="x">The luma sample X coordinate.</param>
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/// <param name="y">The luma sample Y coordinate.</param>
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/// <returns>The leaf coding-unit depth.</returns>
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public int GetDepth(int x, int y) |
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=> this.depths.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2]; |
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/// <summary>Gets the effective luma quantization parameter at a luma sample coordinate.</summary>
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/// <param name="x">The luma sample X coordinate.</param>
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/// <param name="y">The luma sample Y coordinate.</param>
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/// <returns>The effective luma quantization parameter.</returns>
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public int GetQuantizationParameter(int x, int y) |
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=> this.quantizationParameters.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2]; |
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/// <summary>Gets a value indicating whether the coding unit at a luma sample coordinate bypasses transform and quantization.</summary>
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/// <param name="x">The luma sample X coordinate.</param>
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/// <param name="y">The luma sample Y coordinate.</param>
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/// <returns><see langword="true"/> when bypass is enabled; otherwise, <see langword="false"/>.</returns>
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public bool IsTransquantBypass(int x, int y) |
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=> (this.flags.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2] |
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& TransquantBypassFlag) != 0; |
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/// <summary>Gets a value indicating whether the coding unit at a luma sample coordinate contains PCM samples.</summary>
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/// <param name="x">The luma sample X coordinate.</param>
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/// <param name="y">The luma sample Y coordinate.</param>
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/// <returns><see langword="true"/> for pulse-code-modulated samples; otherwise, <see langword="false"/>.</returns>
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public bool IsPcm(int x, int y) |
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=> (this.flags.DangerousGetRowSpan(y >> this.MinCodingBlockLog2)[x >> this.MinCodingBlockLog2] |
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& PcmFlag) != 0; |
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/// <summary>Releases the owned coding-tree state maps.</summary>
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public void Dispose() |
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{ |
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this.depths.Dispose(); |
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this.quantizationParameters.Dispose(); |
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this.flags.Dispose(); |
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} |
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/// <summary>Divides a nonnegative sample count by a power of two with upward rounding.</summary>
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/// <param name="value">The sample count.</param>
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/// <param name="shift">The base-two divisor logarithm.</param>
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/// <returns>The upward-rounded quotient.</returns>
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private static int DivideCeilingByPowerOfTwo(int value, int shift) => (value + (1 << shift) - 1) >> shift; |
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} |
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